The trailing edge flaps of a high performance airplane have to perform two functions, namely: (a) to provide a high lift-to-drag takeoff configuration; and (b) to provide a high lift coefficient landing configuration. A high lift to drag ratio for takeoff can be accomplished by trailing edge flap position with (a) high Fowler motion (i.e. aft flap motion which increases wing projected area, and (b) small flap deflection angles. The high lift coefficient for landing requires (a) significent Fowler motion, and (b) high flap deflection angles. Theoretically, the best Fowler motion versus flap deflection angle results when the flap initially moves rearwardly with little or no deflection, and at the end of its rearward travel deflects downwardly into the landing configuration.
The mechanism that guided and drives the flaps from the stowed to the takeoff and landing positions is generally located underneath the flaps. It is quite common for present commercial aircraft to have single, double or triple slotted flaps that travel in a curved track to position the flaps in the desired flight configuration. While this arrangement provides optimum flap positions for takeoff and landing using low drag fairings, the flap track supports are heavy and have inherent in-service problems with track wear and jamming.
Typical design problems encountered with flap assemblies for modern jet cylindrical aircraft involve weight, size and complexity. In general, it is necessary to increase the side and weight of flap support components in order to increase the strength of the flap assembly to support heavy aircraft, such as the Boeing 747, which require high lift flaps to land at high gross weights on short runways. The increased weight of the aircraft makes it more expensive to operate in terms of fuel expanded. The increased size of the flap assembly components, some of which are located exterior to the wing and enclosed by aerodynamically "smooth" fairings, results in increased drag which causes increased fuel expenditure and reduced aircraft operating performance. Some short to medium range aircraft are equipped with double slotted flaps, mounted from a single hinge below the wing. This flap configuration is designed to provide very high lift coefficients for landing where takeoff lift coefficients and lift to drag ratios are not critical. To minimize cruise drag, the flap assembly and fairing enclosing it should have a small cross-sectional area.
There is a need, however, for flap systems which have the aerodynamic advantages associated with track guided flap assemblies, yet without the weight, size and serviceablility problems encountered with conventional track guided flap assemblies. Specifically, there are flap assemblies which provide adequate Fowler motion for various flap extensions, while requiring a relatively small flap support fairing to reduce cruise drag. The sophisticated flap motion of these conventional systems is generally accomplished utilizing a complex system of links, tracks and drive assemblies which not only greatly increase the gross weight of the aircraft, but are also more prone to wear and to failure. Some conventional flap assemblies utilize a linear fore and aft track to support a mobile carriage assembly thereon which in turn supports the aircraft flaps. To achieve a high lift flap capable of supporting large aerodynamic loads, the flap assemblies, and particularly the track and support assemblies, must be quite heavy. In addition, to achieve the required flap angles and Fowler motion, it is often necessary to use more than one track and carriage assembly further adding to the overall weight and size (i.e. drag) of the flap assembly. Additional weight comprising a drive mechanism in the form of complex links, gears and cams is added to the aircraft to positon the carriage assemblies along the track and in turn to position the flaps in the desired flight configuration.
In U.S. Pat. No. 3,112,089--Dornier, there is disclosed an airplane wing flap assembly comprising two flaps in a fore and aft configuration which are pivotally rotated between the retracted and deployed positions.
In U.S. Pat. No. 4,434,959--Rudolph, there is disclosed a trailing edge flap assembly comprising a flap member supported by a mobile track which in turn is supported by a stationary mounted slide block.
In U.S. Pat. No. 4,353,517--Rudolph, there is disclosed a trailing edge flap assembly comprising a flap member which is mounted for longitudinal slide motion relative to a fixed mounting structure.
In U.S. Pat. No. 4,381,093--Rudolph, there is disclosed a flap assembly comprising two flaps which are pivotally rotated between the retracted and deployed positions by two four-bar linkages.
Other patents cited in a search conducted in association with preparation of the present application include U.S. Pat. Nos. 2,146,014--Grant; 2,973,069--Morse; 2,584,038--Morrison; 2,137,879--Ksoll; and Italian Patent No. 350,474.
There is needed, therefore, an aircraft flap assembly which provides the desired Fowler motion, which is of reduced weight and size to decrease aircraft gross weight and airfoil drag, and which is relatively simple in order to increase operational reliability.